This invention relates to a damper arrangement and in particular relates to a damper blade and means to selectively control the opening and closing of a flow through orifice to provide a selectively buffered transition in a system when starting or stopping fluid flow.
It is desirable to provide for a buffered transition when removing a fluid system from or returning a fluid system to full fluid flow. For example, in the filtering of a gas stream using cloth fabric bags, it is desirable to avoid a sudden surge of fluid when a fluid controlling damper arrangement is activated since sudden surges of fluid may cause the fabric filter bag to snap and consequently weaken the fabric material and cause other undesirable results. This weakening of the fabric is particularly noticeable when the fabric material contains glass fibers or components therein. The prior art damper arrangements, such as bullseye dampers and butterfly dampers, can only be made to function satisfactorily in controlling sudden surges of fluid by using an expensive time actuating means which causes them to operate very slowly. Even then, butterfly dampers are particularly difficult to use because the fluid flow rate does not change linearly with respect to the change of position of the damper blade, but rather most of the fluid control occurs when the damper blade is merely parallel to the direction of fluid flow. Less objectionable is the bullseye damper since its flow rate changes linearly over the entire damper blade stroke.